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UDEV custom rules

#udev   #linux   #ubuntu  

Table of Content

UDEV custom rules#

Udev (userspace /dev) is a Linux sub-system for dynamic device detection and management. Udev is based on rules Every received device event is matched against the set of rules read from files located in /lib/udev/rules.d

Application and custom rules place under /etc/udev/rules.f folder udev rule files must prefix with number and .rules extension.

device info / udevadm info#

Query the udev database for device information.

udevadm info -a -n <device name>
udevadm info -a -n /dev/sda
udevadm info /dev/sda
- -a: Print all sysfs properties of the specified device that can be used in udev rules to match the specified device. It prints all devices along the chain, up to the root of sysfs that can be used in udev rules. - -n: The name of the device node or a symlink to query (/dev/sda)

custom rule#

rule info query#

udevadm info
udevadm info /dev/sda                
P: /devices/pci0000:00/0000:00:14.0/usb3/3-1/3-1.3/3-1.3:1.0/host0/target0:0:0/0:0:0:0/block/sda
N: sda
L: 0
S: disk/by-id/usb-LG_FlashDrive-0:0
S: disk/by-uuid/63AC-7AA5
S: disk/by-path/pci-0000:00:14.0-usb-0:1.3:1.0-scsi-0:0:0:0
S: disk/by-label/my_data
E: DEVPATH=/devices/pci0000:00/0000:00:14.0/usb3/3-1/3-1.3/3-1.3:1.0/host0/target0:0:0/0:0:0:0/block/sda
E: DEVNAME=/dev/sda
E: DEVTYPE=disk
E: DISKSEQ=36
E: MAJOR=8
E: MINOR=0
E: SUBSYSTEM=block
E: USEC_INITIALIZED=3012112447
E: ID_VENDOR=LG
E: ID_VENDOR_ENC=LG\x20\x20\x20\x20\x20\x20
E: ID_VENDOR_ID=0ea0
E: ID_MODEL=FlashDrive
E: ID_MODEL_ENC=FlashDrive\x20\x20\x20\x20\x20\x20
E: ID_MODEL_ID=2168
E: ID_REVISION=2.00
E: ID_SERIAL=LG_FlashDrive-0:0
E: ID_TYPE=disk
E: ID_INSTANCE=0:0
E: ID_BUS=usb
E: ID_USB_INTERFACES=:080650:
E: ID_USB_INTERFACE_NUM=00
E: ID_USB_DRIVER=usb-storage
E: ID_PATH=pci-0000:00:14.0-usb-0:1.3:1.0-scsi-0:0:0:0
E: ID_PATH_TAG=pci-0000_00_14_0-usb-0_1_3_1_0-scsi-0_0_0_0
E: ID_FS_LABEL=my_data
E: ID_FS_LABEL_ENC=my_data
E: ID_FS_UUID=63AC-7AA5
E: ID_FS_UUID_ENC=63AC-7AA5
E: ID_FS_VERSION=FAT16
E: ID_FS_TYPE=vfat
E: ID_FS_USAGE=filesystem
“P:” Device path in /sys/
“E:” Device property
“S:” Device node symlink

udevadm info output prefixes full list

write custom rule#

SUBSYSTEM=="usb", ACTION=="add", ENV{DEVTYPE}=="usb_device",  RUN+="/usr/local.bin/trigger.sh"
- == : compare for equality - += : add value to a key that holds a list of entries. - ACTION - SUBSYSTEM - ENV{DEVTYPE} - RUN : execute a script - SYMLINK: create symlink for the device (under /dev folder)

Note

  • todo: check again Script must location /usr/local/bin/, /bin,

reload rules#

udevadm control --reload

Tip

Sometimes it’s better to reboot

Reference#